Add problem 501 .

1 files changed, 58 insertions, 0 deletions

diff --git a/cpp/501.cpp b/cpp/501.cpp
new file mode 100644
index 0000000..197ed10
--- /dev/null
+++ b/cpp/501.cpp
@@ -0,0 +1,58 @@
+#include <cstddef>
+#include <vector>
+
+using std::vector;
+
+struct TreeNode
+{
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+};
+
+class Solution
+{
+public:
+    void dfs(TreeNode *node, int &last, int &count, int &max_count, vector<int> &result)
+    {
+        if (node == nullptr)
+            return;
+
+        dfs(node->left, last, count, max_count, result);
+
+        auto current = node->val;
+        if (current == last)
+        {
+            count += 1;
+        }
+        else
+        {
+            count = 1;
+        }
+
+        if (count == max_count)
+        {
+            result.push_back(current);
+        }
+        else if (count > max_count)
+        {
+            max_count = count;
+            result.clear();
+            result.push_back(current);
+        }
+
+        last = current;
+        dfs(node->right, last, count, max_count, result);
+    }
+
+    vector<int> findMode(TreeNode *root)
+    {
+        if (root == nullptr)
+            return {};
+        int last = 0, count = 0, max_count = 0;
+        vector<int> result;
+        dfs(root, last, count, max_count, result);
+        return result;
+    }
+};